Jack fruit is the only fruit that grows also from the tree trunk. What makes this possible?

The jackfruit tree bears fruits in the trunks or near the base of older branches from where the female flowers emerge in the first place. Given that jackfruit is the heaviest among the tree borne fruits, reaching up to 35 kg in weight, it is possible that the trees bear them in the trunk or older branches that are strong enough to hold the fruit. 

Another example is the durian tree, which is commonly found in south-east Asia. Durain fruits can weight up to 4 kg and emerge in large clusters from the trunk. Both jackfruit and durain have thick pedicels that hold these large fruits. Jackfruit trees bear male and female flowers in separate flower - heads.

 

The male flowers appear in new growth among the leaves above the female flowers. Female flowers appear on short, stout twigs emerging from the base of the trunk or large branches; sometimes even from the base of the tree under the soil. 

Durain flowers appear as a cluster and have bisexual flowers borne on short, thick twigs. The stigma (female part) matures much earlier than the another bearing stamens (male part) enabling cross-pollination. 

Courtesy : The Hindu